The development of small-size and diversified electronics causes a great restriction in space and safety. Apparently, conventional planar circuit boards cannot meet requirements of many fields on electronics any more. Hence, multilayer or stepped circuit boards have arisen and have gradually taken the place of conventional planar circuit boards. However, for those skilled in the art, there is always a challenge to fabricate a stepped circuit board of a three-dimensional structure design. Particularly, during the fabrication of a stepped groove thereof, there will be depressions or projections, adhesive flowing or other defects. In addition, if a stepped groove is not appropriate in design, the processes, such as printing patterns on the outer layer of a circuit board, dry film laminating, drilling and solder-masking, will be more difficult.